Most thermostat valves used in automotive engines for controlling the flow of coolant to an engine have a very serious deficiency. The thermal element controlling these valves is a plastic plug that is supposed to expand and open the valve whenever the engine coolant rises above a threshold temperature. However, when that plug becomes damaged or disintegrates, it fails to expand and thus the valve remains in its closed position. That permanently blocks the flow of cooling water to the engine. If the operator does not turn the engine off, the engine continues to overheat, causing serious, permanent damage and most likely a stranded motorist. That can be very frustrating and expensive, considering that the cause is the failure of a relatively inexpensive engine part.
Many attempts have been made to design fail-safe devices that will cause thermostat valves to remain open when they fail. Examples of such fail-safe valves are shown in U.S. Pat. Nos. 3,498,537; 3,558,046; 4,245,782; 4,883,225; 4,981,260; 5,174,496 and 5,188,287. However, the fail-safe mechanisms of these valves rely on thermal elements that are under tensile or bending stress. These elements are prone to premature breaking, thus shortening the expected life of the valves. In addition, most fail-safe valves are relatively complicated and expensive to manufacture. For these reasons, the thermostat valves commonly used on today's automobiles and trucks are of the conventional type that remain closed when their thermal elements fail.